[gnome-applets/wip/windowpicker] windowpicker: fix item assignment on workarea change

[Sebastian Geiger <segeiger src gnome org>]

commit a76ce282647184142e9a1492e5d6c21a82d46f01
Author: Sebastian Geiger <sbastig gmx net>
Date:   Sun Dec 9 17:16:56 2018 +0100

    windowpicker: fix item assignment on workarea change
    
    This fixes a long standing issue on multi-monitor setups.
    When a panel moves to another monitor then the assignment
    of task items to the task list needs to be recomputed.
    
    This patch fixes the issue by listening for changes
    of the workarea and reinitializes the task lists.

 configure.ac                 |   5 ++
 windowpicker/src/Makefile.am |   2 +
 windowpicker/src/task-list.c | 115 +++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 117 insertions(+), 5 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 358c4f49c..a6dc9a2a8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -121,6 +121,11 @@ PKG_CHECK_MODULES(GNOME_APPLETS, libpanel-applet >= $LIBPANEL_REQUIRED)
 AC_SUBST(GNOME_APPLETS_CFLAGS)
 AC_SUBST(GNOME_APPLETS_LIBS)
 
+dnl -- check for X11 (required) -----------------------------------------------
+PKG_CHECK_MODULES([X11], [x11])
+AC_SUBST(X11_CFLAGS)
+AC_SUBST(X11_LIBS)
+
 AC_ARG_WITH([libpanel-applet-dir], [], [LIBPANEL_APPLET_DIR=$withval], [LIBPANEL_APPLET_DIR=""])
 if test "$LIBPANEL_APPLET_DIR" == ""; then
        LIBPANEL_APPLET_DIR=`$PKG_CONFIG --variable=libpanel_applet_dir libpanel-applet`
diff --git a/windowpicker/src/Makefile.am b/windowpicker/src/Makefile.am
index 352e159c4..cb55229cd 100644
--- a/windowpicker/src/Makefile.am
+++ b/windowpicker/src/Makefile.am
@@ -13,6 +13,7 @@ libwindow_picker_applet_la_CFLAGS = \
        -I$(top_srcdir) \
        $(GNOME_APPLETS_CFLAGS) \
        $(LIBWNCK_CFLAGS) \
+       $(X11_CFLAGS) \
        $(GCC_FLAGS) \
        $(WARN_CFLAGS) \
        $(AM_CFLAGS) \
@@ -27,6 +28,7 @@ libwindow_picker_applet_la_LDFLAGS = \
 libwindow_picker_applet_la_LIBADD = \
        $(GNOME_APPLETS_LIBS) \
        $(LIBWNCK_LIBS) \
+       $(X11_LIBS) \
        $(LIBM) \
        $(NULL)
 
diff --git a/windowpicker/src/task-list.c b/windowpicker/src/task-list.c
index 312f59c60..5ddcde2d5 100644
--- a/windowpicker/src/task-list.c
+++ b/windowpicker/src/task-list.c
@@ -23,6 +23,7 @@
 
 #include <libwnck/libwnck.h>
 #include <panel-applet.h>
+#include <X11/Xlib.h>
 
 struct _TaskListPrivate {
     WnckScreen *screen;
@@ -32,6 +33,15 @@ struct _TaskListPrivate {
 G_DEFINE_TYPE_WITH_PRIVATE (TaskList, task_list, GTK_TYPE_BOX);
 
 static GSList *task_lists;
+static gboolean has_filter;
+guint size_update_event_source;
+
+static gboolean
+on_monitors_changed (gpointer user_data);
+
+static GdkFilterReturn window_filter_function (GdkXEvent *gdk_xevent,
+                                               GdkEvent *event,
+                                               gpointer user_data);
 
 static TaskList *
 get_task_list_for_monitor (TaskList *task_list,
@@ -61,11 +71,8 @@ static void on_task_item_closed (
     TaskItem *item,
     TaskList *list)
 {
-    gtk_container_remove (
-        GTK_CONTAINER (list),
-        GTK_WIDGET (item)
-    );
-    gtk_widget_destroy (GTK_WIDGET (item));
+    gtk_container_remove (GTK_CONTAINER (list),
+                          GTK_WIDGET (item));
 }
 
 static gint
@@ -238,6 +245,9 @@ task_list_class_init(TaskListClass *class) {
 
     obj_class->dispose = task_list_dispose;
     obj_class->finalize = task_list_finalize;
+
+    task_lists = NULL;
+    has_filter = FALSE;
 }
 
 static void task_list_init (TaskList *list) {
@@ -276,6 +286,16 @@ GtkWidget *task_list_new (WpApplet *windowPickerApplet) {
     g_signal_connect (taskList->priv->screen, "window-opened",
             G_CALLBACK (on_window_opened), taskList);
 
+    if (!has_filter)
+      {
+        has_filter = TRUE;
+
+        gdk_window_add_filter (gtk_widget_get_window (GTK_WIDGET (taskList)),
+                               window_filter_function,
+                               taskList);
+      }
+
+
     GList *windows = wnck_screen_get_windows (taskList->priv->screen);
     while (windows != NULL) {
         on_window_opened (taskList->priv->screen, windows->data, taskList);
@@ -296,3 +316,88 @@ task_list_get_monitor (TaskList *list)
     return gdk_screen_get_monitor_at_window (gdk_screen,
                                              gdk_window);
 }
+
+static void
+remove_task_item (GtkWidget *item, gpointer list)
+{
+  g_return_if_fail (TASK_IS_LIST (list));
+
+  gtk_container_remove (GTK_CONTAINER (list), item);
+}
+
+static gboolean
+on_monitors_changed (gpointer user_data)
+{
+  GList *current_list = task_lists;
+
+  while (current_list != NULL)
+    {
+      TaskList *list = current_list->data;
+      GdkWindow *window = gtk_widget_get_window (GTK_WIDGET (list));
+      gint list_monitor;
+
+      g_signal_handlers_block_by_func (list->priv->screen,
+                                       on_window_opened,
+                                       list);
+
+      list_monitor = gdk_screen_get_monitor_at_window (gdk_screen_get_default (),
+                                                       window);
+
+      if (task_list_get_monitor (list) == list_monitor)
+        {
+          gtk_container_foreach (GTK_CONTAINER (list), remove_task_item, list);
+        }
+
+      GList *windows = wnck_screen_get_windows (list->priv->screen);
+
+      while (windows != NULL)
+        {
+          on_window_opened (list->priv->screen, windows->data, list);
+          windows = windows->next;
+        }
+
+      g_signal_handlers_unblock_by_func (list->priv->screen,
+                                         on_window_opened,
+                                         NULL);
+
+     current_list = current_list->next;
+    }
+
+  size_update_event_source = 0;
+
+  return G_SOURCE_REMOVE;
+}
+
+static GdkFilterReturn window_filter_function (GdkXEvent *gdk_xevent,
+                                               GdkEvent *event,
+                                               gpointer user_data)
+{
+  XEvent *xevent = (XEvent *) gdk_xevent;
+
+  switch (xevent->type)
+    {
+      case PropertyNotify:
+        {
+          XPropertyEvent *propertyEvent;
+
+          propertyEvent = xevent;
+
+          const Atom WORKAREA_ATOM = XInternAtom (propertyEvent->display,
+                                                  "_NET_WORKAREA", True);
+
+          if (propertyEvent->atom != WORKAREA_ATOM)
+            return GDK_FILTER_CONTINUE;
+
+          if (size_update_event_source != 0)
+            return GDK_FILTER_CONTINUE;
+
+          size_update_event_source = g_idle_add (on_monitors_changed,
+                                                 user_data);
+
+          break;
+        }
+      default:break;
+    }
+
+  return GDK_FILTER_CONTINUE;
+}